Download Biogeochemical cycles lec. notes.doc

Biogeochemical cycles
1.
All substances in organisms cycle through ecosystems.
a. The bulk of these are not contained within the bodies of organisms.
1.
Contained within the atmosphere: C, N, O
2.
Contained within rocks: P, K, others
2.
The water cycle
a. All life depends directly on the presence of water.
b. Energy from the sun powers the evaporation of water into the atmosphere.
1.
Most of it falls back into the oceans or subsurface bodies of
water.
2.
98% of earths water is free, only 2% is fixed.
Plants obtain water from the earth.
Animals drink water or obtain it by eating plants.
Water occurs as surface and ground water.
a. Aquifers are permeable saturated layers of rock, sand and gravel.
b. Ground water is an important reservoir of water.
c. Water table: the unconfined portion of ground water.
Groundwater flows more slowly than surface water.
a. Rate of human use is increasing enormously.
b. Many aquifers are threatened with depletion.
Pollution in groundwater is a serious problem.
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The carbon cycle
Based on atmospheric carbon dioxide.
Synthesis of organic compounds is accomplished by photosynthesizers.
a. All heterotrophic organisms depend on their activity.
3. Carbon dioxide is released into the atmosphere when organisms decompose.
4. Some carbon compounds are accumulated.
a. Cellulose is more resistant to breakdown.
b. May eventually be incorporated into fossil fuels or minerals.
1.
1000 billion metric tons of CO2 are dissolved in the ocean.
2.
Fossil fuels contain 500 billion metric tons.
3.
600 – 100 billion metric tons are contained within organisms.
5. Processes of respiration and photosynthesis are roughly balanced.
a. CO2 is increasing as a result of burning fossil fuels and the destruction of
forests.
b. Result: Global warming and the greenhouse effect.
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Nitrogen cycle
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8.
Nitrogen gas constitutes 78% of the atmosphere.
Very little nitrogen is fixed in the soil, oceans and organisms.
Few organisms convert atmospheric nitrogen into biologically useful forms.
a. All are nitrogen fixing bacteria.
b. Triple bond linking nitrogen atoms makes the gas very stable.
Some nitrogen fixing bacteria are free-living.
Some form symbiotic relationships with plants.
Nitrification
a. Nitrifying bacteria oxidize ammonia to nitrates, and release energy.
b. Plant cells reduce nitrate to ammonia to make nitrogen compounds, like
amino acids.
Bacteria and fungi rapidly decompose nitrogen containing compounds.
a. Ammonification: release of excess ammonium.
Fixed nitrogen is lost to the atmosphere by denitrification.
Oxygen cycle
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3.
Only the earth possesses significant quantities of free oxygen.
Free oxygen is the product of three billion years of photosynthesis.
Without the continuous photosynthesis, respiration would deplete all nonatmospheric oxygen within 50 years.
Phosphorous cycle
1.
2.
Most biogeochemical cycle reservoirs are mineral in nature.
Phosphate exists in the soil in only small amounts.
a. Are relatively insoluble and contained in only certain kinds of rocks.
b. Weather out of rocks, transported to the oceans.
c. Brought up by natural uplift of land masses or by marine animals
d. Form rich deposits of guano from sea birds.
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Millions of tons of phosphate are added to farmland each year.
Absorption of phosphorus in many plants is aided by fungal mycorrhizae.
Large quantities of phosphorous are carried to the sea each year.
Gaia hypothesis
1.
Organisms have evolved with the physical environment to provide an intricate
control system that keeps life earth’s conditions favorable for life (Lovelock,
1979)
The chemistry of the atmosphere and earth’s strongly buffered physical
environment are utterly different from conditions on any other planet in the solar
system.
3. From the very beginning organisms played the major role in the development and
control of a geochemical environment favorable to themselves.
4. Atmosphere:
Earth w/o life
with life
CO2
98%
.03%
Nitrogen
1.79%
79%
Oxygen
trace
21%
Surface temp
290 +/- 50 C
13 C
2.
pH: Ammonia produced in soils produces a pH in soils that is favorable to life.